Nitrogen (N) in terrestrial ecosystems is stored in soil organic matter, soil may function as a long-term N sink or pool.

Intensive human activity, however, results in land degradation, leading to a rapid decline in soil N due to the decomposition and erosion.

Soil degradation and loss of the soil N stock may be reversed by vegetation restoration.

Furthermore, the accumulation of soil carbon (C) is supported by the input of additional N, such that sustained soil C sequestration depends largely on the availability of soil N after ecological restoration. It follows that understanding of soil N sequestration following vegetation restoration is important for understanding global C and N cycles.

Researchers from the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) collected data from 358 fixed points in the karst catchment in China to determine the trends, magnitude, and mechanisms of soil N sequestration after 10 years of revegetation.

They found that, topsoil N concentration increased significantly, whereas soil N density changed negligibly after 10 years of vegetation restoration.

"The bedrock exposure affected the change in soil N concentration and the soil N sequestration value (ΔND) via affecting the change in soil C concentration, by directly affecting bulk density, soil depth, and Ca2+,” said Prof. WANG Kelin, a researcher in ISA.

"The soil C:N ratio increased significantly in the overall catchment and in most restoration types and was strongly related to ΔND, which suggests that the coupled relationship between accumulation of soil C and N was controlled by the sequestration of soil N,” WANG added.

The team also found that ΔND was significantly related to the change in soil C:N ratio, indicating that the coupling between soil C and N may be constrained by insufficient soil N sequestration during revegetation.

These findings suggest that the restoration of degraded karst ecosystems requires an increase in soil N input early during vegetation restoration.

This work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, the Youth Innovation Promotion Association of Chinese Academy of Sciences, and the Youth InnovationTeam Project of ISA, CAS.

The study entitled “Changes in soil nitrogen stocks following vegetation restoration in a typical karst catchment” has been published in Land degradation & development, details could be found at https://doi.org/10.1002/ldr.3204 

Contact: WANG Kelin

E-mail: kelin@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences